Fcc yield selectivity improvements in high containment riser termination systems

ABSTRACT

The invention provides an improved system for separation technology intended to reduce unwanted catalyst/thermal reactions by minimizing contact of the hydrocarbons and the catalyst within the reactor.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of, and claims priority to,and the benefit of U.S. application No. 15/833,107, filed Dec. 6, 2017,titled “FCC YIELD SELECTIVITY IMPROVEMENTS IN HIGH CONTAINMENT RISERTERMINATION SYSTEMS,” which claims the benefit of U.S. ProvisionalApplication No. 62/430,512, filed Dec. 6, 2016, titled “FCC YIELDSELECTIVITY IMPROVEMENTS IN HIGH CONTAINMENT RISER TERMINATION SYSTEMS,”each of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Fluidic catalytic cracker (FCC) reactor technology has evolved over theyears, continuously searching to improve yield selectivity ofhydrocarbons by minimizing unwanted reactions that occur outside of theFCC riser. Most FCC reactors use a catalyst which is an extremely porouspowder that reacts with the hydrocarbon mixture to capture intermetalcarbon and metal. In the process, the pre-heated hydrocarbon feed mixedwith hot catalyst enters the reactor through one or more risers. Theriser creates a fluidized bed where a concurrent upward flow of reactantgases and catalyst particles occurs. Nearly every FCC unit employs sometype of separation device connected on the end of the riser which isintended to separate the bulk of the catalyst from the hydrocarbonvapors. The technology includes riser termination devices which rangefrom providing a physical downward deflection of the catalyst as itexits the riser to directly attaching the riser outlet to sets ofcyclones. The most commonly used separation devices are vortexseparation systems (VSS) and vortex disengager stripper systems (VDS).The vortex separation system includes a tube with a split head locatedat the riser outlet to separate the mixture. The VDS system has astripping unit at the bottom of a rough vortex evaporation system andusually forms two stage stripping.

Gases leave the reactor through the cyclones after separation from thepowdered catalyst. The gas is then passed to a fractionator forseparation into the product streams. The spent catalyst is commonly sentto a regenerator unit and is regenerated by combusting carbon depositsto carbon dioxide. The regenerated catalyst is returned to the reactorfor further use. Separation of the gases from the catalyst is seldomtotally efficient, whereas gases and catalyst may tend to recirculate inthe separation device creating conditions resulting in over crackedgases and over fouling of the catalyst. The present invention providesan improved system for the VSS/VDS technology intended to reduceunwanted catalytic/thermal reactions by minimizing contact of thehydrocarbons and the catalyst outside of the riser.

SUMMARY OF THE INVENTION

This invention reduces the amount of undesired thermal and catalyticreactions occurring in FCC reactors having high containment separationsystems such as the VSS/VDS. The undesired reactions are exacerbated byhydrocarbon underflow in the separation system, resulting in increasedresidence time between the hydrocarbon vapors and the catalyst. It isdesirable to limit the time during which the hydrocarbon vapors andcatalysts are intermixed. The longer the mixing time, the more potentialfor lower hydrocarbon yields and greater catalyst fouling. If thecatalyst is too fully entrained with hydrocarbon vapors as it exits theriser and enters the separation technology, the hydrocarbon vapor willnot cleanly separate from the catalyst and will carry under with thecatalyst resulting in hydrocarbon underflow to the catalyst bed, leadingto unwanted thermal and catalytic reactions. The present inventionmitigates these unwanted reactions and improves FCC yield by minimizinghydrocarbon underflow into the separation system. In essence, the bottomof the separation system sits in a catalyst bed that preventshydrocarbon vapor from remixing with the catalyst in the separationsystem. Vent tubes provide an exit path for the hydrocarbon vaporexiting the stripper to bypass the separation system and exit thereactor via the cyclones.

The cyclone operations must be carefully monitored to ensure thatcyclone inlet hydrocarbons are not dragged downward by the catalyticsolids.

Historically, increasing the amount of catalyst inventory contained inthe reaction prevents such under flow or back flow of hydrocarbon gases.However, the structures of the present invention create an environmentwherein increased hydrocarbon gas yield can be associated with lessercatalyst inventory, less catalyst entrainment into the separation systemand less resultant hydrocarbon underflow.

The structure of the present invention and a resulting use of decreasedcatalyst inventory produces efficient FCC operations with less consumedenergy.

IN THE DRAWINGS

FIG. 1 is a schematic of a FCC reactor incorporating a first embodimentof the present invention.

FIG. 2 is a schematic of an FCC reactor incorporating another embodimentof the invention.

FIG. 3 is a schematic of a FCC reactor incorporating yet anotherembodiment of the present invention.

FIG. 4 is a graphical representation of catalyst temperature response todecreased catalyst levels in the reactor.

FIG. 5 shows the results of two test runs of the present invention.

FIG. 6 is a graph of the results of varying the catalyst bed elevationfor a variety of fluidized bed density levels for the test runs of FIG.5.

FIGS. 7a-i are product yield graphs at varying catalyst bed levels inthe reactor for the test runs of FIG. 5.

FIG. 8 shows the results of a third test run of the present invention onanother FCC reactor at a different location.

FIG. 9 shows the dry gas and regenerator temperature shifts at varyingcatalyst bed levels for the test of FIG. 8.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Referring now to FIG. 1, a schematic depicting a FCC reactorincorporating a first embodiment of the invention is shown having alowered fluidized catalyst bed 22 maintained just above the windows 32of the separator or VSS 14. The reactor 10 includes an inlet 12 forreceiving a mixture of heated crude oil and heated catalyst. The crudeand catalyst mixture travels up the riser 13 during which the catalystand crude interact and the catalyst absorbs carbon, metals, and otherdeleterious materials not wanted in the hydrocarbon gases. As theentrained hydrocarbon/catalyst mixture exits the riser and enters theseparator 14 the catalyst will fall downward through the separator 14while the clean hydrocarbon stream continues to rise where it isreceived by cyclones 16 which serve to further separate any remainingcatalyst from the hydrocarbon stream. The cleansed hydrocarbon streamthen exits the reactor through outlet 18 to be transferred to separationequipment, such as a fractionator. The separated catalyst located in thecyclone flows down the dipleg 20 and is reentered into the catalyst bed22. Any hydrocarbon gases that become entrained with the fallingcatalyst will reenter the fluidized catalyst bed 22 for furtherseparation and those gases will flow upwardly as shown by flow arrows H.The catalyst bed 22 is fluidized by high pressure steam being injectedin the reactor 10 through steam inlet 26. The spent catalyst will exitthe reactor at exit 24 and, most commonly, will be sent to a regeneratorfor cleansing. The regenerated catalyst is then reentered with the crudemixture at inlet 12.

The hydrocarbon gases that become entrained with the falling catalystenter the fluidized catalyst bed and are processed until they becomecleansed hydrocarbon gases. The cleansed hydrocarbon gases will risethrough the separator and will be captured by the cyclones 16.

In the prior art at FCC units, not shown, there is a common effect atthe lower level of the separator 14, wherein the hydrocarbon gases andcatalyst recirculate above the fluidized bed 22. This recirculationcreates an inefficiency in the operation of the reactor as the catalystand hydrocarbons continue to react, resulting in decreased hydrocarbonyield and increased catalyst fouling. Increased catalyst fouling leadsto increased heat expenditure when the catalyst is sent to theregenerator for cleansing. Increased regenerator temperatures createinefficiencies in the operation of the system. The present inventionseeks to solve the catalyst/hydrocarbon recirculation issues in thelower portion of the separator 14.

In the prior art, not shown, the fluidized bed 22 was maintained wellabove the top of the separator windows 32, preferably at 180 incheswater column (“IWC”). In the FIG. 1 embodiment the fluidized bed hasbeen lowered to approximately 150 IWC and yield has been improved asexhibited in FIGS. 4-9.

The reactor of FIG. 1 is shown having the top level of the catalyst bed22 located directly above the windows 32 of the separator 14. Referringto FIG. 3, it can be seen that when the catalyst bed level in thereactor ranges between 130 and 160 IWC or directly above the separator14 windows 32, the catalyst temperature being delivered from theregenerator is much lower, resulting in higher efficiencies.

Referring now to FIG. 5, the yield results from two test runs of thepresent invention on the same FCC reactor, for the various productsproduced by the catalytic cracking are shown. The yield plots on thetables show total hydrocarbon production increasing or remaining stableas the result of decreased overall cracking due to the lower bed levelsfor the catalyst. Delta coke is also decreased indicating more valuableproduct being recovered. Due to increased product recovery and decreasedover cracking, the reactor operations are made more efficient.

FIG. 6 graphically represents proposed more efficient operating levelsfor the catalyst bed elevation, using a variety of fluidized bed densitylevels. The most efficient operating levels range from 125 IWC for theleast dense fluidized catalyst to 170 IWC for the most dense fluidizedcatalyst. The catalyst bed levels are optimally located just above theVSS windows 32.

FIGS. 7a-i show the product yield graphs for the tests of FIG. 5. Duringthe first test, the reactor outlet temperature was 970° F. compared witha reactor outlet temperature of 950° F. during the second test. Thedifference in reactor outlet temperature is the reason for the offsetsin the yields shown in FIGS. 7a-i . Again, it can be seen that lowercatalyst bed levels result in increased yield and decreasedtemperatures.

Referring now to FIG. 2, the FCC unit is shown having the top level ofthe catalyst bed 22 located below the windows 32 of the separator 14.Under proper gas flow rates and hydraulic balance, hydrocarbon gaseswill bypass the separator 14 and exit the reactor, loweringhydrocarbon/catalyst residence time in the separator 14.

Referring now to FIG. 3, the invention provides another alternativestructure to assist in the effort to separate clean hydrocarbon gasesfrom the fluidized catalyst efficiently. The alternative structureincludes a baffle member 28 positioned immediately under the separator14. The structure allows for the optimal level for the catalyst bed 22to be further lowered as shown. Baffle 28 prevents any fluidizedcatalyst from entering the separation chamber 14. Hydrocarbon gasesescape the fluidized bed after residence in the stripper 15 andfluidized bed 22 through vent tubes 30 which carry the clean hydrocarbongases directly to the upper most region of the separator, allowing thosegases to be passed to the cyclones 16.

Another example of a test run of the present invention at a differentlocation and on a different reactor from that as shown in FIG. 5 isshown in FIG. 8. The data shown in FIG. 8 and FIG. 9 proves improvedyield selectivities and the dry gas and regenerator temperature shiftsassociated with lower catalyst inventory. The delta yields for a 26-28%lowered catalyst inventory in the reactor shows significant improvement.In both volume percent and weight percent.

The above detailed description of the present invention is given forexplanatory purposes. It will be apparent to those skilled in the artthat numerous changes and modifications can be made without departingfrom the scope of the invention. Accordingly, the whole of the foregoingdescription is to be construed in an illustrative and not a limitativesense, the scope of the invention being defined solely by the appendedclaims.

1. The process for increasing hydrocarbon yield and decreasing cokeproduction in an FCC reactor having a separation unit and at least onechamber window, wherein the bottom of the separation unit is spacedapart from a bed of fluidized catalyst, comprising the step of locatingthe bed of fluidized catalyst level in the FCC reactor such that the bedof fluidized catalyst is directly above the at least one chamber windowsof the separation unit.
 2. The process of claim 1 wherein the catalystbed level falls within the range of 125 IWC to 170 IWC.
 3. The processof claim 1 wherein the catalyst bed density is 32.8 lbs/ft³ at anoperating level of 125 IWC at an elevation of 164 ft.
 4. The process ofclaim 1 wherein the catalyst bed density is 36.9 lbs/ft³ at an operatinglevel of 140 IWC at an elevation of 164 ft.
 5. The process of claim 1wherein the catalyst bed density is 41 lbs/ft³ at an operating level of150 IWC at an elevation of 164 ft.
 6. The process of claim 1 wherein thecatalyst bed density is 45.1 lbs/ft³ at an operating level of 170 IWC atan elevation of 164 ft.
 7. The process of claim 1 wherein the distancebetween the bottom of the separation unit and the top of the catalystbed is maximized to prevent fluidized catalyst from entering the bottomof the separator unit.
 8. The process of claim 1 wherein fluidizedcatalyst is prevented from entering the separation unit by means of abaffle member positioned between the bottom of the separation unit andthe top of the fluidized bed.
 9. The process of claim 1 whereinhydrocarbon gases evacuate from the fluidized bed after residence in thecatalyst through at least one vent tube which carry the cleanhydrocarbon gases directly to the top region of the separator unit. 10.A process for increasing hydrocarbon yield and decreasing cokeproduction in an FCC reactor having a separation unit comprising:spacing apart a bed of fluidized catalyst from the separation unit;locating the bed of fluidized catalyst level in the FCC reactor at alocation immediately above an at least one chamber windows of theseparation unit; positioning a baffle member positioned between theseparation unit in the top of the fluidized catalyst bed; and utilizingat least one vent tube to carry clean hydrocarbon gases directly to atop region of the separator unit.
 11. The process of claim 10 Whereinthe optimum bed level falls within the range of 130 IWC to 160 IWC. 12.The process of claim 10 wherein the catalyst bed density is 41 lb/ft³ atan operating level of 150 IWC at an elevation of 164 ft.
 13. A processfor increasing hydrocarbon yield and decreasing coke production in anFCC reactor having a separation unit comprising: spacing apart a bed offluidized catalyst from the separation unit; locating the bed offluidized catalyst level in the FCC reactor at a location immediatelyabove at least one chamber windows of the separation unit; and utilizingat least one vent tube to carry clean hydrocarbon gases directly to thetop region of the separator unit.
 14. The Process of claim 13 whereinthe optimum bed level range falls within the range of 130 IWC to 160IWC.
 15. The process of claim 13 wherein the catalyst bed density is 41lb/ft³ at an operating level of 150 IWC at an elevation of 164 ft.